1. Field of the Invention
The present invention relates to improvement in the structure of the auxiliary valve mechanism of a sliding exhaust brake system which is installed in the exhaust pipe of a large-sized vehicle, such as a truck or bus, and acts to close off the exhaust passage for the exhaust gas flowing through the exhaust pipe when the vehicle is going down steep hills, thereby braking the vehicle.
2. Description of the Prior Art
The present inventor et al. filed U.S. Pat. Ser. No. 146,841 on Jan. 22, 1988, for an auxiliary valve mechanism that is used in an exhaust brake system of this kind. This valve mechanism is shown in FIGS. 8-10, where the auxiliary valve mechanism, indicated by numeral 17, is fixed to the front end of a piston rod 16. A support frame 18 of a substantially C-shaped cross section is mounted to the front surface of a fixed block member 20 located near the front end of the rod 16. The frame 18 engages with a valve member 15 provided with an exhaust pressure-adjusting hole 14. A liner 19 is mounted loosely inside the frame 18 and makes a frictional contact with the bottom wall of the valve member 15. Both longitudinal ends of the liner 19 are bent upwardly. The auxiliary valve mechanism 17 is buried in the frame 18 and in the liner 19.
Generally, the aforementioned sliding exhaust brake system has an air cylinder system incorporating a coil spring that urges the piston rod upward at all times. When the brake system operates, the coil spring is caused to expand and contract repeatedly. As a result, the piston and the piston rod are rotated.
In the above-described known auxiliary valve mechanism 17, since the liner 19 is loosely mounted and buried in the support frame 18, the frame 18 swings in response to the rotation of the piston. Therefore, one or both longitudinal ends of the frame 18 are rubbed against the surface of the valve member 15 and also against the inner surface of the housing of the body of the exhaust brake, as shown in FIG. 10. As a result, they locally wear away or get damaged. Then, the operation is not performed satisfactorily. Also, the lifetime of the manufactured product is shortened. Hence, it cannot be used for a long period.